Process for the flotation of sulfide ores

ABSTRACT

Process using collectors for the flotation of minerals which allow the separation or enrichment of certain minerals, even at pH values around 7. These collectors are organic sulphides of the type R--S--R&#39;, in which the two groups R and R&#39; are different and at least one of them preferably carries a substituent including oxygen or sulphur. The collectors are desirably used in a proportion of 10-100 ppm in relation to the weight of the mineral subject to flotation.

DESCRIPTION

The present invention relates to collectors or flotation agents for theflotation of minerals. It relates particularly to a series ofthio-organic compounds having a pronounced affinity for variousminerals, particularly sulphides, enabling improvements to be made inthe flotation of these substances.

Flotation, which has been of very great service in the enrichment ofminerals and has attained an advanced degree of development at thepresent time, comprises the utilization of certain specific substanceswhich are capable of rendering hydrophobic the mineral or minerals whichare to be flotated. Such substances as are currently employed includexanthates, dithiophospates, dithiocarbamates, sulpho-succinamates,mercaptans, benzotriazole and mercaptobenzothiazole. Though some ofthese collectors give good results, there is still a desire to improveflotation, in order better to separate the desired minerals from theirgangue and to obtain them in better yields and with better selectivity.Such an advance is realised by the present invention. It provides a newseries of substances capable of serving as collectors in flotation, withimproved yields of valuable species. While they are applicable tovarious kinds of minerals, the collectors according to the invention areparticularly suitable for the separation of sulphide minerals, forexample galena, chalcopyrite, argentite, chalcocite, covellite, pyritesand marcasite. Owing to their specificity of action, the substancesaccording to the invention provide a good separation between certainminerals; for example, they permit the separation of chalcopyrite frompyrites or from blende more effectively than can be done with knowncollectors.

FIG. 1 represents a graph of the recovery rate for galena plotted as afunction of the pH of the pulp.

FIG. 2 represents graphs of the recovery rates of chalcopyrite andblende as a function of pH.

FIG. 3 represents graphs showing the recovery rates of various sulfideores including differences with respect to their corresponding gangues.

The collectors according to the invention are organic sulphides,particularly asymmetric dialkyl sulphides. Preferably, at least one ofthe organic groups, particularly one of the alkyl groups, carries asubstituent of a different nature from these groups.

The flotation agents of the invention can be represented by the formula:

    R--S--R'

in which the groups R and R' are different from one another and each canbe a saturated or unsaturated organic radical, more particularly a C₁ toC₂₀ hydrocarbon radical. The latter can be acyclic, alicyclic oraromatic. The acyclic radicals can be aliphatic, ethylenic or evenacetylenic. Thus, the above formula can be of the type:

    C.sub.x H.sub.y --S--C.sub.x.sbsb.1 H.sub.y.sbsb.1 --H,

    C.sub.x H.sub.y --S--C.sub.x.sbsb.1 H.sub.y.sbsb.1 --OH

or

    C.sub.x H.sub.y --S--C.sub.x.sbsb.1 H.sub.y.sbsb.1 --COOR"

where R" is H, a cation such as Na, K, NH₄, Ca etc. or a C₁ to C₁₈hydrocarbyl group and more particularly a C₁ to C₄ alkyl group. In theseformulae, x is an integral number from 2 to 20 and y is one from 2 to41. x₁ is 1 to 18 and is always lower than x, while y₁ is 2 to 37 and isalways lower than y. The compounds which are most preferred and also theeasiest to produce are those in which C_(x) H_(y) is a straight orbranched C₂ to C₁₈ alkyl group, preferably a C₆ to C₁₈ alkyl group,while C_(x).sbsb.1 H_(y).sbsb.1 is a C₁ to C₆ alkenyl group.

In one embodiment of the invention, one or more of the oxygen atomsattached to the --C_(x).sbsb.1 H_(y).sbsb.1 -- group is/are replaced byone or more sulphur atoms, which thus gives a thiol function--C_(x).sbsb.1 H_(y).sbsb.1 --SH or a thio-ester or thio-acidC_(x).sbsb.1 H_(y).sbsb.1 CSOR", --C_(x).sbsb.1 H_(y).sbsb.1 --CSSR".

By way of example, very good collectors are constituted by sulphides inwhich R' is of the form:

    --(CH.sub.2).sub.n --OH  or  --(CH.sub.2).sub.n COOR"

where n can be from 1 to 18 and particularly 1 to 6, while R" is ahydrocarbon group, particularly a C₁ to C₁₈ alkyl group.

Thus, among the flotation agents according to the invention, particularcompounds are of the type R--S(CH₂)_(n) OH or R--S--(CH₂)_(n) --COOR",comprising substances such as, for example:

    __________________________________________________________________________    C.sub.6 H.sub.13 --S--CH.sub.2 CH.sub.2 CH.sub.2 OH,                                              C.sub.8 H.sub.17 --S--CH.sub.2 CH.sub.2 CH.sub.2 OH,      C.sub.8 H.sub.15 --S--CH.sub.2 CH.sub.2 OH,                                                       C.sub.10 H.sub.21 --S--CH.sub.2 OH,                       C.sub.12 H.sub.25 --S--CH.sub.2 CH.sub.2 OH,                                                      C.sub.18 H.sub.37 --S--CH.sub.2 OH,                       C.sub.6 H.sub.13 --S--CH.sub.2 --CH.sub.2 --CH.sub.2 --COOCH.sub.3,                               C.sub.14 H.sub.29 --S--CH.sub.2 CH.sub.2 COOC.sub.2                           H.sub.5,                                                  C.sub.14 H.sub.29 --S--CH.sub.2 CH.sub.2 SH,                                                      C.sub.14 H.sub.29 --S--CH.sub.2 CH.sub.2 COOH,            C.sub.12 H.sub.25 --S--CH.sub.2 CH.sub.2 COONa,                                                   C.sub.16 H.sub.33 --S--CH.sub.2 CH.sub.2 CSSNH.sub.2,                         1                                                         C.sub.12 H.sub.25 --S--CH.sub.2 CH.sub.2 CSOH,                                                    C.sub.16 H.sub.33 --S--CH.sub.2 CH.sub.2 COOH             __________________________________________________________________________                        etc.                                                  

The technique of flotation is well known to persons skilled in the artat the present time and thus does not need to be explained here. Thecollectors according to the invention are applicable within the scope ofthis known technique, so that it is unnecessary to change the conditionsemployed.

The collectors according to the invention can be employed in very lowproportions. It is generally sufficient to provide 10 to 500 ppm withrespect to the mineral undergoing flotation and most often about 30 to200 ppm or 30 to 200 g/tonne. In relation to the volume of the pulp tobe treated, this proportion is 0.5×10⁻⁴ to 25×10⁻⁴ g/l or 0.05 to 2.5ppm.

An important factor in the application of flotation adjuvants is the pHof the pulp of the minerals to be treated. For each particular collectorin its application to a given mineral under predetermined conditions,there generally corresponds an optimum pH which the skilled person willhave no difficulty in establishing. Most often, the rates of recovery ofnumerous minerals are higher at low pH values, particularly at or below5. For certain minerals, for example pyrites, the rate drops sharply atpH values above 7, particularly above 8, and in this circumstance, it isbetter to separate these minerals from certain others by alkalinisationof the pulp. These general properties of collectors are also found whenmaking use of the products according to the invention. However,variations in the rate of recovery as a function of pH, found with theadjuvants of the application, follow different curves from those ofknown collectors. They permit recovery and/or separation of mineralswhich is better than is given with standard adjuvants.

Whether it relates to the overall flotation of valuable species or todifferential flotation for the separation of such species from oneanother, the collectors according to the invention are capable ofincreasing the efficacy of operation with respect to prior adjuvants. Inparticular, variations in the rate of recovery as a function of pH oftenallow a mineral to be obtained in a better yield at a pH aroundneutrality, which thus avoids the cost of acidification oralkalinisation of the pulp. On the other hand, as the difference betweenthe rates of flotation of two different minerals is greater than withstandard collectors, separation of these minerals is more effective.Examples 12 and 13 below illustrate these advantages of the invention.

The non-limiting examples which follow illustrate the application of theinvention to various particular minerals. The mode of operation used inthese examples comprises the treatment of a pulp constituted by 1 g ofmineral in particles of 63 to 160 microns in 300 ml of water, the pulpbeing placed in a Hallimond cell. Under magnetic agitation, sulphuricacid or caustic soda solution is added in order to adjust the pH of thepulp to the desired value. After the addition of an appropriate quantityof the mercapto-ethanolic derivative in solution of ethyl alcohol to thepulp, a current of nitrogen at about 10 l/h is passed into the base ofthe cell through a No. 3 fritted filter. The flotation operation per seis effected for 3 minutes. The particles of the mineral entrained to thesurface are recovered, dried and weighed. This thus determines thepercentage quantity recovered by flotation of this mineral with respectto the pulp treated.

With the exception of Example 3, in which 0.5 ml of a 1/1000 alcoholicsolution of the collector was utilised, all the other tests wereeffected with 0.1 ml of such a solution, which corresponds to 100 g ofcollector per tonne of mineral. By way of comparison, no collector wasadded in the case of Example 1. All the tests were effected at ambienttemperature. The table below gives the results of these tests.

    ______________________________________                                                                            % of mineral                              Example No.                                                                            Mineral  Collector   pH    recovered                                 ______________________________________                                        1        Galena   none        3     10                                        2        "        Dodecyl-2-thio-                                                               ethanol     4     97                                         3*      "        Dodecyl-2-thio-                                                               ethanol     9.5   94                                        4        "        Tetradecyl-2-                                                                 thio-ethanol                                                                              3.5   82                                        5        Chalco-  Dodecyl-2-thio-                                                      pyrite   ethanol     4     95                                        6        Chalco-  Dodecyl-2-thio-                                                      pyrite   ethanol     10    78                                        7        Chalco-  Tetradecyl-2-                                                        pyrite   thio-ethanol                                                                              3.5   85                                        8        Blende   Dodecyl-2-thio-                                                               ethanol     4     44                                        9        "        Dodecyl-2-thio-                                                               ethanol     10    29                                        10       "        Tetradecyl-2-                                                                 thio-ethanol                                                                              3.5   29                                        11       Pyrites  Tetradecyl-2-                                                                 thio-ethanol                                                                              3.5   50                                        ______________________________________                                         *used 0.5 ml of solution of collector per thousand.                      

These results show that, by adequate adjustment of the pH, sharpseparations of certain minerals can be obtained. For example, it ispossible to separate chalcopyrite from pyrites better than by processesutilizing known collectors. It should be noted in this connection thatpotassium amyl xanthate, utilized in the prior art, only allows about92% of chalcopyrite to be obtained (U.S. Pat. No. 4,022,686, Col. 14).

EXAMPLE 12

This example is illustrated by FIG. 1 of the accompanying drawing, whichrepresents the graph of recovery rate for galena, plotted as a functionof the pH of the pulp subjected to flotation.

Comparative flotation tests, similar to those of the foregoing Examples,were effected using galena with the xanthate collector known in the artas "PAX" (potassium amyl xanthate) and with one of the productsaccording to the invention, dodecyl-2-thio-ethanol,

    C.sub.12 H.sub.25 --S--CH.sub.2 CH.sub.2 OH

It is known that flotation with the same collector can give variableresults depending upon the origin and particle size range of themineral, as well as the operative details. Thus, in order to havecomparable conditions, in the present example, operation was carried outrigorously in the same fashion in the two series of tests (1) and (2),on two portions of the same galena pulp. The curve GA-1 was plotted fromthe percentage of galena recovered by flotation in the presence ofdodecyl-2-thio-ethanol at different pH values. GA-2 is the correspondingcurve obtained with the xanthate ("PAX") as the collector.

In the two cases, the quantities of collector were 80 g per tonne ofgalena. It can be seen that at a pH of about 4.8, the two collectors ledto the same rate of recovery of 76%. But at pH=7.5,dodecyl-2-thio-ethanol (GA-1) still gave 75% recovery, while with thexanthate (GA-2) this fell to a minimum of 40%. Thus, it is at pH valuesin the region of 7 that operation is most economical, as acidificationor alkalinisation of the pulp is not required.

Dodecyl-2-thio-ethanol thus has a marked advantage over xanthate. Itpermits recovery of galena in good yields over the whole pH range from5.5 to 9 and particularly from 6 to 8.

EXAMPLE 13

FIG. 2 represents graphs of the rates of recovery of chalcopyrite andblende as a function of pH.

As in Example 12, completely comparable flotation tests were effected onthe two minerals indicated:

CH-1: chalcopyrite with dodecyl-2-thio-ethanol,

CH-2: chalcopyrite with "PAX" xanthate,

BL-1: blende with dodecyl-2-thio-ethanol,

BL-2: blende with "PAX" xanthate. p It will be noted that, at pH valuesabove about 5, the curve CH-2 of FIG. 2 passes below CH-1, that is tosay at these pH values the flotation yield of chalcopyrite withdodecyl-2-thio-ethanol is greater than that given with the knownxanthate collector.

The contrary is given for blende, the curve BL-2 being above BL-1. Itthus follows that the difference between the curves CH-1 and BL-1 isgreater than that between CH-2 and BL-2. This shows that the separationof chalcopyrite from blende is greater by flotation in the presence ofdodecyl-2-thio-ethanol than with xanthate. Thus, for example at pH 7.5,the percentages of mineral recovered are:

    ______________________________________                                                                         differ-                                                      chalcopyrite                                                                           blende  ence                                         ______________________________________                                        with xanthate (CH--2-BL--2)                                                                     87.5       68      19.5                                     with C.sub.12 H.sub.25 --S--CH.sub.2 CH.sub.2 OH                              (CH--1-BL--1)     94         64      30                                       ______________________________________                                    

There is thus a gradient of 30 instead of 19.5 which contributes to theenrichment of chalcopyrite accompanied by blende, when utilizing as thecollector the product according to the invention in place of the usualxanthate. To arrive at the same result with the latter, it is necessaryto adjust the pH to about 9.5, which requires a supplementary operationwith supply of the basic reactant. It can be seen that, contrary tostandard collectors, those of the invention give recoveries ofchalcopyrite superior to 90% over a range of pH values from 6 to 8, thatis to say in the vicinity of neutrality.

EXAMPLE 14

By the same method as in the foregoing Examples, the percentage ofrecovery of galena by flotation was determined, on the one hand, withdodecyl methyl sulphide, C₁₂ H₂₅ SCH₃, and on the other, with thestandard "PAX" xanthate. The proportion of collector was calculated soas to represent 80 g per tonne of pulverised galena. The table belowgives the percentage of mineral recovered at different pH values of thepulp.

    ______________________________________                                        pH       C.sub.12 H.sub.25 SCH.sub.3                                                                    Xanthate                                            ______________________________________                                                 %                %                                                   5        75.0             75.0                                                6        64.5             52.5                                                7        52.5             41.0                                                8        56.0             42.5                                                9        60.0             50.0                                                ______________________________________                                    

These results show that, starting at pH 5, the sulphide according to theinvention gave better rates of recovery than the usual collector.

The sulphide of this Example can be replaced by other analagous R--S--R'sulphides, where R is a C₁₂ to C₁₈ alkyl group and R' is a C₁ to C₆alkyl group.

EXAMPLE 15

The technique of the foregoing Examples was applied to flotation testsin the presence of myristyl-thia-acetic acid, that is to saytetradecyl-thia-methylene-carboxylic acid, or tetradecyl-thia-2-aceticacid C₁₄ H₂₉ --S--CH₂ COOH.

The proportion of this collector was 80 g per ton of mineral. Withchalcopyrite at pH values of 4.5 to 6, the results were still betterthan for the collectors according to the invention of the precedingExamples. As FIG. 3 shows, the rate of flotation then attained 98%.

For blende, there was a rapid fall at pH 5.5 and an even more abrupt onefor pyrites above pH 3.5. These facts are very interesting since theyallow an excellent separation of these minerals from chalcopyrite orfrom galena. FIG. 3 clearly illustrates this advantage. This figure alsoshows the facility with which the useful minerals separate from quartzand dolomite.

It is to be noted that the tests at pH values above 7 are affected afterthe addition of NaOH to the pulp. It can thus be considered that in thiscase the collector is in the form of its sodium salt, C₁₄ H₂₉ --S--CH₂COONa.

EXAMPLE 16

Flotations effected as in Example 15, but with dodecyl-thiaacetic acid,C₁₂ H₂₅ --S--CH₂ COOH, in place of myristyl-thiaacetic acid led tosimilar results, but with a decrease in the percentage of mineralrecovered at pH>7 which was:

greater for chalcopyrite,

less for galena, blende and pyrites.

Thus, the following percentages were found:

    ______________________________________                                                  pH 5.5   pH 7       pH 10                                           ______________________________________                                        chalcopyrite                                                                              96           95.5     86                                          galena      89         80         20                                          blende      82         45         12                                          pyrites     55         16          7                                          ______________________________________                                    

This shows the extended possibilities for the collectors according tothe invention. According to needs in each particular case, it ispossible to choose a suitable thio compound of R and R' appropriate tothe task to be effected.

EXAMPLE 17

Following the mode of operation of the foregoing Examples, flotationtests for chalcopyrite were effected with 100 g of palmityl-thia-aceticacid, C₁₆ --H₃₃ --S--CH₂ COOH, at 100 g per tonne of mineral and, inparallel, with 100 g per tonne of potassium amyl-xanthate ("PAX"-knowncommercial collector).

The following percentages of mineral recovered, as a function of pH werefound:

    ______________________________________                                        pH   C.sub.16 H.sub.33 SCH.sub.2 COOH                                                            K amyl-xanthate                                                                            Without collector                             ______________________________________                                        4.25 93            91           31                                            5    92            87           26                                            6    85            73           19                                            7    72            62           16                                            8    73            66           17                                            9    76            80           21                                            10   86            88           23                                            ______________________________________                                    

It will be seen that up to pH 8, palmityl-thia-acetic acid is clearlymore advantageous than the known xanthate.

We claim:
 1. A process of flotation of sulphide minerals, by using 10 to500 ppm of a collector comprising a thio-organic compound, with respectto the weight of the mineral to be flotated, wherein the collector is anorganic sulfide of the type R--S--(CH₂)_(n) --OH, in which R is a C_(x)H_(y) hydrocarbon radical where x is an integer from 2-20 and y is aninteger from 2-41 and in which n is an integer from 1-18.
 2. A processof flotation of one or more sulfide minerals according to claim 1, whichcomprises forming a pulp with said collector, establishing a desired pH,and effecting flotation.
 3. A process according to claim 2, wherein themineral is at least one of chalcopyrite and galena and is carried outwith the pH of the pulp adjusted to 6 to
 8. 4. A process according toclaim 1 in which x is an integer from 2-18 and n is an integer of 1-6.5. A process according to claim 4 in which x is an integer of 6-18.
 6. Aprocess according to claim 5 in which the amount of the collector is30-200 ppm.
 7. A process according to claim 5 or 6 in which the pH is3.5-10.
 8. A process according to claim 7 in which said collector isdodecyl-2-thio-ethanol or tetradecyl-2-thio-ethanol.